Two of the central concepts in understanding descent with modification are analogy and homology. Analogy is where different anatomical structures are used to solve the same biomechanical problem. An example of analogy are the differences between the bat wing and the bird wing. While these structures share the same function, a cursory examination of each reveals that they are composed of different skeletal elements and are constructed differently. This, in conjunction with the known information that bats are mammals and birds are in the class Aves, strongly suggests that these structures are not evolutionary related. Homology is similarity of structures due to common descent. An example of this would be the primate arm and bat wing, both of which are constructed from the same anatomical features.
The writers of OPAP get this concept wrong from the get go. On page 115, they write:
The Darwinian definition of homology, however, does not rest upon the two parts being identical, or even similar for that matter, in appearance or function. Darwinists have defined homology as correspondence of structure derived from a common primitive origin, a definition that assumes macroevolution to be true.
For starters, it was the overwhelming evidence of homology in the natural world that allowed Darwin to formulate his theory of descent with modification in the first place. The authors correctly state that homology as a concept had been around since before Darwin's time. Darwin simply used the concept of homology, he did not redefine it.
On page 124, they write this about homology:
But consider how limited the usefulness of the concept is; it cannot replace subjective judgments, nor can it deliver us from the influences of our presuppositions. Notice that the truth of Darwinism must be assumed before such an assessment of relationship can be made. Marsupial pouches and bones are considered homologous because it is assumed that the organisms possessing them descended from a common ancestor.
This is exactly backward. The fact that the animals display homologous traits indicates that they share a common ancestor. Linnaeus formulated his binomial taxonomy based on relationships between organisms based on homology. All palaeontologists do is extrapolate that concept into the past to make inferences about descent.
On the next page, they write:
Why were not the North American placentals given the same bones [as the marsupials]? Would an intelligent designer withhold these structures from placentals if they were superior to the placental system? At present we do not know; however, we all recognize that an engineer can choose any of several different engineering solutions to overcome a single design problem.
We don't know? If something has been intelligently designed, it ought to be obvious, like the truck in the middle of the field. If the placental system is better than the marsupial system and yet the marsupial system is the norm in Wallacea (Australia and New Zealand), how intelligent is that? The only reason the marsupial system is the norm in Wallacea is that the Wallace Trench prevents placentals from entering the region. Where they are transported to the region by other (more modern) means, they outcompete the marsupials for resources--hence the "Rabbit-Proof Fence."
In the "A Note to Teachers" section, the authors state that:
Since the 1970s, for example, scientific criticisms of the long-dominant neo-Darwinian theory of evolution (which combines classical Darwinism with Mendelian genetics) have surfaced with increasing regularity.
The sources the authors cite are an amazingly diverse lot. Four of them are creationist sources, Six are general sources and several are journal articles. Three were published prior to 1970. I have read most of the journal articles and they do not criticize the domiant neo-Darwinian theory of evolution as defined here. There are questions about the tempo and mode of evolution but all evolutionary biologists assume that genetics play an important role. The authors do not define "classical Darwinism." This is a standard creationist ploy--make a blanket statement and then support it with references that are either outdated or do not necessarily support what they are saying.
On page 154, the authors state:
In the spirit of good, honest science, Pandas makes no bones about being a text with a point of view. Because it was intended to be a supplemental text, the authors saw no value in simply rehashing the orthodox accounts covered by basal textbooks.
"In the spirit of good, honest science..."? Since when is it good, honest science to promote a particular viewpoint? Science goes where the evidence leads, not where you hope it will lead. Then you report what you find and integrate it into a larger body of knowledge about a particular field.
On page 155, the authors pull the old "double shuffle." They state:
Many people assert that evolution in this second sense [descent with modification] is a fact, just as gravity is a fact. But the two situations are hardly analagous . The fact of gravity can be verified simply by dropping a pencil--an experiment anyone can perform. Common ancestry, however, cannot be directly verified by such an experiment.
In the first part of this section, the authors mention "descent with modification." In the last part, they talk about " common ancestry." The two are not the same. Descent with modification can be observed in just about any population of organisms. A change in gene frequencies from one generation to the next is "descent with modification." This is basic evolutionary theory. It is the theoretical extrapolation through time across the species boundary that the authors object to and they have lumped it all together.
There is this goody on page 160:
For example, the mutational events that allegedly produced reptiles, birds, mammals, and even humans have never been observed--nor will they ever be observed. Similarly, the transitional life forms that occupy the branching-points on Darwin's tree of life are also unobservable. Transitional forms exist now only as theoretical entities that make possible a coherent Darwinian account of how present-day species originated.
By this reasoning, no fossil form could ever be transitional. So when we find Archaeopteryx, with its reptilian body plan and hollow arm bones and feathers, this is not transitional. It is simply a form of animal that was created by divine fiat--despite what its existence STRONGLY suggests.
Other scientists have reviewed this book and a list of those reviews can be found here. These usually proceed from specific subject areas of expertise but, when taken together, form a consistent theme: OPAP is bad science and a bad textbook. If this is the current state of Intelligent Design education, then it surely does not belong in a science classroom, First Amendment issues aside. Reading this book was a truly depressing experience and it shows that many creationists have made little to no progress at understanding basic biological concepts in the last seventy years. If your child is in a school district that is using this book or you know of one, alert them immediately!! This book should be avoided.